Tidal Range Energy Resource and Optimization – Past

1 Tidal range energy resource and optimization { past 2 perspectives and future challenges a,∗ b a 3 Simon P. Neill , Athanasios Angeloudis , Peter E. Robins , Ian c a d a 4 Walkington , Sophie L. Ward , Ian Masters , Matt J. Lewis , Marco a b b f 5 Piano , Alexandros Avdis , Matthew D. Piggott , George Aggidis , Paul g h f e 6 Evans , Thomas A. A. Adcock , Audrius Zidonisˇ , Reza Ahmadian , Roger e 7 Falconer a 8 School of Ocean Sciences, Bangor University, Marine Centre Wales, Menai Bridge, UK b 9 Department of Earth Science and Engineering, Imperial College London, UK c 10 School of Natural Sciences and Psychology, Department of Geography, Liverpool John 11 Moores University, Liverpool, UK d 12 College of Engineering, Swansea University, Bay Campus, Swansea, UK e 13 School of Engineering, Cardiff University, The Parade, Cardiff, UK f 14 Engineering Department, Lancaster University, Lancaster, UK g 15 Wallingford HydroSolutions, Castle Court, 6 Cathedral Road, Cardiff, UK h 16 Department of Engineering Science, University of Oxford, Oxford, UK 17 Abstract 18 Tidal energy is one of the most predictable forms of renewable energy. Al- 19 though there has been much commercial and R&D progress in tidal stream 20 energy, tidal range is a more mature technology, with tidal range power plants 21 having a history that extends back over 50 years. With the 2017 publication 22 of the \Hendry Review" that examined the feasibility of tidal lagoon power 23 plants in the UK, it is timely to review tidal range power plants. Here, we 24 explain the main principles of tidal range power plants, and review two main 25 research areas: the present and future tidal range resource, and the opti- 26 mization of tidal range power plants. We also discuss how variability in the 27 electricity generated from tidal range power plants could be partially offset 28 by the development of multiple power plants (e.g. lagoons) that are comple- Preprint∗Corresponding submitted toauthor Renewable Energy May 2, 2018 Email address: [email protected] (Simon P. Neill) 29 mentary in phase, and by the provision of energy storage. Finally, we discuss 30 the implications of the Hendry Review, and what this means for the future 31 of tidal range power plants in the UK and internationally. 32 Keywords: Tidal lagoon, Tidal barrage, Resource assessment, 33 Optimization, Hendry Review, Swansea Bay 34 Contents 35 1 Introduction 3 36 2 A brief history of tidal range schemes 7 37 2.1 Commercial progress . .7 38 2.1.1 Current schemes . .7 39 2.1.2 Proposed schemes . .9 40 2.2 Engineering aspects of tidal range power plants . 10 41 3 Numerical simulations of tidal range power plants 12 42 3.1 0D modelling . 12 43 3.2 1D modelling . 14 44 3.3 2D and 3D models . 15 45 3.4 Observations and validation . 19 46 4 Tidal range resource 20 47 4.1 Theoretical global resource . 20 48 4.2 Theoretical resource of the European shelf seas . 22 49 4.3 Non-astronomical influences on the resource . 26 50 4.4 Long timescale changes in the tidal range resource . 27 2 51 4.5 Socio-techno-economic constraints on the theoretical resource . 28 52 5 Optimization 31 53 5.1 Energy optimization . 31 54 5.2 Economic optimization . 33 55 5.3 Implications of regional hydrodynamics for individual lagoon 56 resource . 34 57 5.4 Multiple lagoon resource optimization . 35 58 6 Challenges and opportunities 37 59 6.1 Variability and storage . 37 60 6.2 Additional socio-economic benefits through multiple use of space 39 61 6.3 Implications of the Hendry Review . 40 62 7 Conclusions 42 63 1. Introduction 64 Much of the energy on Earth that is available for electricity generation, 65 particularly the formation of hydrocarbons, originates from the Sun. This 66 also includes renewable sources of electricity generation such as solar, wind 67 & wave energy, and hydropower (since weather patterns are driven, to a 68 significant extent, by the energy input from the Sun). However, one key 69 exception is the potential for electricity generation from the tides { a result 70 of the tide generating forces that arise predominantly from the coupled Earth- 3 1 71 Moon system . The potential for converting the energy of tides into other 72 useful forms of energy has long been recognised; for example tide mills were 73 in operation in the middle ages, and may even have been in use as far back as 74 Roman times [1]. The potential for using tidal range to generate electricity 75 was originally proposed for the Severn Estuary in Victorian times [2], and 76 La Rance (Brittany) tidal barrage { the world's first tidal power plant { has 77 been generating electricity since 1966 [3]. However, only very recently has the 78 strategic case for tidal lagoon power plants been comprehensively assessed, 79 with the publication of the \Hendry Review" in January 2017 [4]. 80 Tidal range power plants are defined as dams, constructed where the 81 tidal range is sufficient to economically site turbines to generate electricity. 82 The plant operation is based on the principle of creating an artificial tidal 83 phase difference by impounding water, and then allowing it to flow through 84 turbines. The instantaneous potential power (P ) generated is proportional 85 to the product of the impounded wetted surface area (A) and the square of 86 the water level difference (H) between the upstream and downstream sides 87 of the impoundment: P / AH2 (1) 88 A tidal range power plant consists of four main components [5, 6]: 89 • Embankments form the main artificial outline of the impoundment, and 90 are designed to have a minimal length while maximizing the enclosed 91 plan surface area. A key factor in designing the embankment is to 1The Sun also has an important role in tides, but its contribution is around half that of the Moon. 4 92 minimise disturbance to the natural tidal flow. 93 • Turbines are located in water passages across the embankment, and 94 convert the potential energy created by the head difference into rota- 95 tional energy, and subsequently into electricity via generators. 96 • Openings are fitted with control gates, or sluice gates, to transfer flows 97 at a particular time, and with minimal obstruction. 98 • Locks are incorporated along the structure to allow vessels to safely 99 pass the impoundment. 100 Tidal range power plants can be either coastally attached (such as a bar- 101 rage) or located entirely offshore (such as a lagoon). The primary difference 102 between the two refers to their impoundment perimeter. There are also 103 coastally-attached lagoons, where the majority of the perimeter is artificial, 104 potentially enabling smaller developments with more limited environmental 105 impacts than barrages { the latter generally spanning the entire width of an 106 estuary. 107 Following construction, the manner and how much of the potential energy 108 is extracted from the tides largely depends on the regulation of the turbines 109 and sluice gates [7]. They can be designed to generate power one-way, i.e. 110 ebb-only or flood-only, or bi-directionally. In one-way ebb generation, the 111 rising tide enters the enclosed basin through sluice gates and idling turbines. 112 Once the maximum level in the lagoon is achieved, these gates are closed, 113 until a sufficient head (hmax) develops on the falling tide. Power is subse- 114 quently generated until a predetermined minimum head difference (hmin), 115 when turbines are no longer operating efficiently. For flood generation the 5 116 whole process is reversed to generate power during the rising tide. In two-way 117 power generation, energy is extracted on both the flood and ebb phases of the 118 tidal cycle, with sluicing occurring around the times of high and low water 119 [8, 9]. A schematic representation of ebb and two-way generation modes of 120 operation is shown in Fig. 1, highlighting the main trigger points during the 121 tidal cycle that dictate power generation. Nonetheless, there are other pos- 122 sible variations of these regimes (e.g. Section 5.1). For example, ebb/flood 123 generation can often be supplemented with pumping water through the tur- 124 bines to further increase the water head difference values, as considered in 125 studies by Aggidis and Benzon [10] and Yates et al. [11]. 126 In this article, we provide a review of tidal range power plants, with a fo- 127 cus on resource and optimization. The following section provides an overview 128 of the history of tidal range schemes from pre-industrialization to present day, 129 including future proposed schemes. Section 3 compares the various modelling 130 approaches used to simulate tidal lagoon or barrage operation (e.g. 0D versus 131 2D models), and Section 4 examines the global tidal range resource, with a 132 particular focus on the northwest European continental shelf, and constraints 133 on the development of this resource. Section 5 examines ways in which tidal 134 range schemes can be optimised, e.g. flood or ebb generation, pumping, and 135 the benefits of concurrently developing multiple tidal range schemes. Finally, 136 in Section 6, we discuss future challenges and opportunities facing tidal range 137 power plants, including variability and storage, and the implications of the 138 Hendry Review. 6 139 2. A brief history of tidal range schemes 140 Tidal range technologies have a long history, especially when compared 141 with less mature ocean energy technologies such as tidal stream and wave 142 energy. Energy has been extracted from the tides for centuries.

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